With the rapid development of flat-panel display technologies, compared with the traditional liquid crystal displays (LCDs), OLED displays not only are lighter and thinner but also have the advantages of self-illumination, low power consumption, no backlight required, no limit on viewing angle, high response speed and the like, and have become the mainstream products of the next generation of flat-panel display technology.
An organic light-emitting layer lamination in each pixel unit of a traditional OLED display panel may include: a substrate, a transparent anode for hole injection, an organic layer formed by organic molecules or organic polymers, a conductive layer for transporting holes from the anode, an emission layer for transporting electrons injected from a cathode, and the cathode for electron injection. The cathode may be transparent or opaque, depending on the type of the organic light-emitting element.
The traditional organic light-emitting elements mainly include a double emission type, a top emission type and a bottom emission type. In the organic light-emitting element of the double emission type, both the cathode and the anode are transparent. As illustrated in FIG. 1A, the organic light-emitting element includes a transparent anode 2, a hole transport layer 3, an emission layer 4, an electron transport layer 5, and a semi-transparent cathode 6, which are formed on a substrate 1 in sequence. In the case of picture display (or light emission), electrons and holes are respectively injected from the cathode 6 and the anode 2, and then meet within the emission layer 4 and are recombined into excitons; and when the excitons jump from the excited state back to the ground state, energy is released in the form of light. As both the cathode and the anode of the organic light-emitting element of the double emission type are transparent, both the upper surface and the lower surface of the organic light-emitting element of the double emission type can emit light. In addition, the light emitting direction of one surface is opposite to that of the other surface, as illustrated in FIG. 1B, resulting in that one surface cannot display information properly. Therefore, the traditional OLED display device usually does not employ the double emission type organic light-emitting element to achieve double-faced display.
As for an OLED display device, in order to achieve double-faced display, two different structures, namely top emission type organic light-emitting elements and bottom emission type organic light-emitting elements, are typically formed in a pixel array of an array substrate respectively for double-faced display. Light of the top emission type organic light-emitting elements is emitted from the transparent cathodes disposed on the top, and hence the pixels including the top emission type organic light-emitting elements can achieve the display of first display contents; light of the bottom emission type organic light-emitting elements is emitted from the transparent cathodes disposed at the bottom, and hence the pixels including the bottom emission type organic light-emitting elements can achieve the display of second display contents. With the combination of the top emission type organic light-emitting elements and the bottom emission type organic light-emitting elements, pixel separation between the picture displayed on the upper surface and the picture displayed on the lower surface can be achieved, and hence the objective of double-faced picture display can be realized. As illustrated in FIG. 1C which is a schematic sectional view of the traditional double emission type OLED display panel, the display panel comprises top emission type organic light-emitting elements 7 and bottom emission type organic light-emitting elements 8; the top emission type organic light-emitting elements 7 and the bottom emission type organic light-emitting elements 8 are combined to form a pixel array which is further disposed between an upper substrate and a lower substrate.